Cathode-ray-tube beam-deflection system



Nov. 18,1958 "A. J. BIGGS 7 2,861,209

CATHODE RAY-TUBE BEAM-DEFLECTION SYSTEM Filed Dec. 1. 1954 TELEVISIONRECEIVER FIG.1

CATHODE-RAY-TUBE BEAM-DEFLECTION SYSTEM 5 Albert J. Biggs, Wembley,England, assignor to Hazeltine Research, Inc., Chicago, 111., acorporation of Illinois Application December 1, 1954, Serial No. 472,403

Claims priority, application Great Britain December 14, 1953 3 Claims.(Cl. 313-76) General This invention relates to cathode-ray-tubebeam-deflection systems and, while it is of general application, it isparticularly useful in such systems as employed in television receivers.

In cathode-ray-tube beam-deflection systems heretofore proposed, theelectron beam generated within the neck of the cathode-ray tube iscaused to scan the image-reproducing surface or display screen whichcloses one end of the enlarged portion of the tube envelope. In suchsystems, it is sometimes difficult with a given shape and size ofenvelope to achieve as large a maximum displacement of the spot formedby the electron beam on the display screen as may be desired, owing tothe possibility of the electron beam hitting the envelope 3 at thejunction between its neck portion and enlarged portion. Such adifliculty may be particularly important in connection with large screentelevision receivers having a directly viewed cathode-ray tube. Also,for a given maximum spot displacement on the display screen, systems ofthe type previously proposed necessitate a greater tube length than isdesirable for many applications.

It is an object of the invention, therefore, to provide a new andimproved cathode-ray-tube beam-deflection system which avoids one ormore of the foregoing limitations of such systems heretofore proposed.

It is another object of the invention to provide a new and improvedcathode-ray-tube beam-deflection system for obtaining greater maximumdeflection of the electron beam without danger of the electron beamstriking the neck of the cathode-ray tube.

It is another object of the invention to provide such a system in asimple and inexpensive way by utilizing leakage fields previouslythought to be a defect in scanning coils.

In accordance with the invention, a cathode-ray-tube beam-deflectionsystem comprises a cathode-ray tube having an image-reproducing surfaceand means for producing an electron beam for scanning the surface. Thesystem also includes deflection means disposed adjacent the neck of thecathode-ray tube for producing a primary deflection field for deflectingthe electron beam to scan the surface and for producing an auxiliarydeflection field for deflecting the electron beam in a directionopposite to that in which it is deflected by the primary deflectionfield, thereby to enable the electron beam to scan a larger area of thesurface without striking the neck of the cathode-ray tube.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawing, and itsscope will be pointed out in the appended claims.

Referring to the drawings:

Fig. 1 is a circuit diagram, partly schematic, of a complete televisionreceiver including a cathode-ray tube atent O 2,861,209 Patented Nov.18, 1958 2 beam-deflection system constructed in accordance with thepresent invention, and

Fig. 2 is a cross-sectional view of a portion of the Fig. 1 systemshowing a deflection-yoke assembly in greater detail.

Description of cathode-ray tube beam-deflection system Referring for themoment to Fig. 1 of the drawing,

a. cathode-ray-tube beam-deflection system constructed producing anelectron beam 25 for scanning the imagereproducing surface 23. The innersurface of the imagereproducing surface 23 is coated with a suitablephosphor material for producing the desired light pattern in response tothe electron-scanning beam.

The means for producing an electron beam 25 in cathode-ray tube 20includes a cathode 26, for producing a supply of electrons, coupled to asuitable potentialsupply circuit of the receiver 10. The latter meansalso includes a control electrode 27 and an accelerating electrode 28disposed adjacent the cathode 26 and coupled to suitablepotential-supply circuits of the receiver 10, the accelerating electrode28 serving to accelerate the electrons towards the image-reproducingsurface 23 while the control electrode 27, in response to videoinformation from the receiver 10, is effective to control the intensityof the electron beam and thereby the brightness of the spot reproducedon the surface 23. The means for producing an electron beam 25 mayfurther utilize a focus winding 29 for focusing the electrons into thedesired narrow beam 25, the winding being connected to suitablefocusing-current circuits of the receiver 10. Additionally, the lattermeans may include a high-voltage terminal 30 which is connected to aconductive coating on the inner surface of the tube envelope and whichis connected to a suitable high-voltage circuit in the receiver 10 toenable the conductive coating to become a second accelerating electrode.

The cathode-ray-tube beam-deflection system, constructed in accordancewith the present invention, also comprises deflection means disposedadjacent the neck 21 of the cathode-ray tube 20 for producing a primarydeflection field for deflecting the electronbeam to scan the surface 23and for producing an auxiliary deflection field for deflecting theelectron beam in a direction opposite to that in which it is deflectedby the primary deflection field, thereby to enable the electron beam toscan a larger area of the surface 23 without striking the neck 21 of thecathode-ray tube 20. The deflection means may comprise, for example, adeflection-yoke assembly 32 having a pair of vertical deflection coilsor windings connected by way of wires 33 and 34 to terminals 35, 35 of asuitable vertical deflection-current circuit of the television receiver10. Similarly, the deflectionyoke assembly 32 includes a pair ofhorizontal deflectioncurrent windings coupled by way of wires 36 and 37to terminals 38, 38 of a suitable horizontal deflection-current circuitof the receiver 10.

As indicated by the more detailed cross-sectional view of Fig 2, thedeflection means preferablyalso includes a core 44 of ferromagneticmaterial so shaped as to provide the desired auxiliary or leakagedeflection field represented, for example, by the field 45 fordeflecting the electron beam in a direction opposite to that in which itis deflected by the primary deflection field represented, for example,by the field 42. The core 44 is in the general form of a shell orcylinder enclosing a portion of the deflection windings as indicatedbyhorizontal. deflection windings 40 and 41. The vert-ical deflectionwindings, not shown in the Fig. 2 cross-sectional view, are effectivelydisposed adjacent the neck 21- of cathode. ray tube 29 at right anglesto the windings 4t} and 41 in a conventional manner. Each of thewindings may be of the conventional saddle type such that it fits thecontour of the tube neck 21. It should be noted that the upper and lowerwindings 40 and 41 are called horizontal" deflection windings becausethe eflect of the magnetic field 42 produced thereby is such as todeflect the electron beam in a horizontal plane. For a similar reasonthe windings, not shown, disposed on either side of the tube neck 21 arecalled vertical deflection windings.

In order to enhance the leakage field 45, segments of ferromagneticmaterial represented, for example, by the upper and lower segments 46and 47 may be located adjacent the tube neck 21 in the path of theleakage field. Similar segments may be disposed on either side of tubeneck 21 in order to enhance the leakage field from the deflectionwindings, not shown, located on either side of the tube neck 21 at rightangles to windings 4t) and 41. These segments do not touch one anotherand must be so shaped as not to misdirect the leakage fields.

Depending on design of the cathode-ray tube, it may be desirable toshape the core 44 so that a leakage field is established by only onepair of the deflection windings, for example, the upper and lowerwindings 40 and 41.

Operation of cathode-ray-tube beam-deflection system Considering theoperation of the cathode-ray-tube beam-deflection system just described,the television receiver 10, including the antenna system 11, 12, iseffective to supply video signals to the control electrode 27 of thecathode-ray tube for controlling the intensity of the electron beam,thereby to control the brightness of the phosphors on the surface 23which are excited by the beam. The television receiver 19 also suppliessuitable potentials and currents to the cathode 26, acceleratingelectrode 28, focus winding 29, and high-voltage terminal 30 forenabling the desired production, acceleration, and shaping of theelectron beam.

The receiver 10 also supplies suitable vertical and horizontaldeflection currents to the vertical and horizontal deflection windingsof the deflection-yoke assembly 32 for enabling the electron beam toscan the image-reproducing surface 23 in both vertical and horizontaldirections, thereby to reproducethe desiredimage.

As indicated by, for example, the horizontal deflection windings and 41of Fig. 2, the deflection currents supplied thereto are eifective toestablish the primary deflection field 42 between the two windings. Theiron core 44 serves as a low reluctance return path for the flux linesof the primary field 42. Because this core 44 does not cover all of theeffective portion of the windings, some of the flux lines towards therear of the windings are enabled to radiate outward from the windings.Some of these lines in establishing a return path cross the axis of thecathode-ray tube in a vertical direction, thereby establishing a leakagefield 45 which may be used for deflection purposes. The ferromagneticsegments 46 and 47 serve to enhance the leakage field 45. Though-notindicated in Fig. 2, vertical-deflection windings establish a similarprimary deflection field at right angles to the horizontal primarydeflection field 42, the vertical deflection windings also establishinga corresponding vertical leakage field at right angles to the horizontalleakage field 45.

In a conventional beam-deflectionsystem, the core corgion B of Fig. 1.

all of the horizontal portion of the deflection windings 40 and 41within region A to prevent leakage fields from occurring. Hence, theelectron beam is deflected only by the deflection field occurring overregion A of the beam path of Fig. 1 in a manner indicated by dashed line25a. As will be noted, for maximum spot displacement on theimage-reproducing surface 23, the electronbeam path indicated by dashedline 25a passes undesirably close to the neck 21 of the cathode-raytube.

In accordance with the present invention, however, the core 44 shown inFig. 2 is so shaped as to provide a leakage field over the portion ofthe beam path lying in re As indicated in Fig. 2, the direction of theleakage field 45 over the region B is opposite to the direction of theprimary deflection field 42 over region A. Thus, as indicated by thesolid line 25b of Fig. l, the electron beam will be deflected by theleakage field in a direction opposite to that in which it is deflectedby the primary deflection. field, the auxiliary deflection due to theleakage field being through a small angle on which. is ubstantiallyproportional to the angle 18 through which. the. electron beam isdeflected by the primary deflection field. When the electron beam comesunder the influence of the primary deflection field, it will, therefore,

be displaced from the axis of the cathode-ray tube in a directionopposite to that in which it is displaced when it reaches the screen 23and, with this arrangement, it is easier to obtain a desired maximumdisplacement of this spot formed by the electron beam on the surface 23without risk of the electron beam hitting the envelope at the junctionbetween its neck portion 21 and enlarged portion 22 than would be thecase with the conventional arrangement in which the electron beam isstill on the axis of the cathode-ray tube when it comes under theinfluence of the primary deflection field. It will, of course, beappreciated that the angle through which the electron beam is deflectedby the leakage field must always be sufliciently small to ensure thatthe electron beam does not hit the neck portion 21 of the envelopebefore coming under the influence of the primary deflection windings 32.

As mentioned, it has heretofore been the practice to eliminate theleakage fields associated with deflection windings as completely aspossible because they were thought to be a defect. It will be noted,however, that the present invention by retaining them and giving themproper magnitude makes use of these leakage fields to achieve adesirable result, namely, greater maximum deflection of the electronbeam for a given set of cathoderay-tube dimensions or vice versa. In sodoing, the desired result is accomplished without adding to the cost ofthe apparatus, additional cost factor being the probable reason Whyother expedients for the same purpose (British Patent 488,188) arecommercially unattractive.

It will also be apparent that the advantages of the present inventionneed not be utilized in both the vertical and horizontal deflectiondirections because .in some applica.- tions increased maximum spotdisplacement on the surface 23 is necessary in only one of thedirections of beam deflection. Also, by enabling a greater maximum spotdisplacement of the electronbeam without danger of the beam striking theneck portion 21 of the cathode-ray tube, the present invention enables agiven size of image to be reproduced by a cathode-ray tube of shorterlength which results from shortening of the length D of the enlargedportion of the. tube envelope.

From the foregoing description of the invention, it will be apparentthat a cathode-ray-tube beam-deflection system constructed in accordancewith the present invention represents an improved system for obtaininggreater maximum deflection of the electron beam.

While there has been described what is at present considered to be thepreferred embodiment of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be made.therein without departing from the invention, and it is, therefore,aimed to cover all such changes and modifications as fall within thetrue spirit and scope of the invention.

What is claimed is:

1. A cathode-ray-tube beam-deflection system comprising: a cathode-raytube having an image-reproducing surface and means for producing anelectron beam for scanning said surface; and deflection means disposedadjacent the neck of the cathode-ray tube for producing a primarydeflection field for deflecting the electron beam to scan said surfaceand for producing an auxiliary deflection field comprising leakage fluxfrom the primary deflection field for deflecting the electron beam in adirection opposite to that in which it is deflected by the primarydeflection field, thereby to enable the electron beam to scan a largerarea of said surface without striking the neck of the cathode-ray tube.

2. A cathode-ray-tube beam-deflection system comprising: a cathode-raytube having an image-reproducing surface and means for producing anelectron beam for scanning said surface; and a deflection coil having amagnetic core disposed adjacent the neck of the cathode-ray tube forproducing a primary deflection field for deflecting the electron beam toscan said surface, the core including means for providing a leakagefield comprising leakage flux from the primary deflection field fordeflecting the electron'beam in a direction opposite to that in which itis deflected by the primary deflection field, thereby to enable theelectron beam to scan a larger area of said surface without striking theneck of the cathode-ray tube.

3. A cathode-ray-tube beam-deflection system comprising: a cathode-raytube having an image-reproducing surface and means for producing anelectron beam for scanning said surface; and a deflection coil having amagnetic core disposed adjacent the neck of the cathode-ray tube forproducing a primary deflection field for deflecting the electron beam toscan said surface, the core including means for providing between thebeam-producing means and the primary field a leakage field comprisingleakage 1 flux from the primary deflection field for deflecting theelectron beam in a direction opposite to that in which it is deflectedby the primary deflection field, thereby to enable the electron beam toscan a larger area of said surface without striking the neck of thecathode-ray tube.

References Cited in the file of this patent

